1. Field of the Invention
The present invention relates to a back-up detecting device with a distance reset capability, and more particularly to a back-up detecting device installable on a large vehicle, which has a capability of measuring an actual distance between the vehicle and an object that the vehicle approaches.
2. Description of Related Art
Most back-up detecting devices employ ultrasonic detection to determine the distance to objects to which a vehicle is approaching. A conventional back-up detecting device is an ultrasonic transmitter and receiver pair or an ultrasonic transceiver installed at the rear of a vehicle. The back-up detecting device emits ultrasonic sound waves. Any object in the field of view of the ultrasonic transmitter will reflect and return ultrasonic waves to the ultrasonic receiver from objects in the detection range of the ultrasonic receiver. The sound waves from the object will be detected, and an alarm will be triggered to warn the driver of an emergency situation.
A rear bumper of a truck is often flush with the body of the truck and is made of steel. Thus installing the detector on the bumper is more difficult. To get around the problem, the detector is attached to the metal chassis underneath the truck. However, the detector may not be flush with the rear of the truck.
With reference to FIG. 6, a conventional back-up detecting device (70) is installed on the chassis underneath a truck (71) forward of the rear end (72). Since sound waves emitted by the detector (70) propagate outward in a conical shape, some of the sound waves are reflected by the chassis of the truck (71) when the detector (70) is installed on the chassis and return to the detector (70). This installation will cause several problems. First the forward displacement of detector may cause the system to misjudge the distance to an object. Second, sound waves reflected by the chassis may trigger false alarms. Finally, the sound waves reflected by the chassis may jam the ultrasonic receiver and keep the receiver from detecting objects.
Some manufacturers use a filter in the detector to separate these noises from regular echoed pulses, but the body structure of each truck is somewhat different, and this is not an adequate solution for all installations.
Back-up detecting devices often employ an intensity analysis program that analyzes intensity of a returned signal to determine the distance to an object, and then use the distance to determine if the object is within a preset threshold range.
Before a detector system can determine a meaningful distance to an object, a distance correction, also known as a distance pad, must be determined for each detector, or a distance error occurs.
For example, a detector (70) detects an object, (80) behind the truck (71) at a measured distance D. However, the detector (70) is installed a distance D′from the rear end (72) of the truck (71), and the object (80) is only a distance (D-D′) from the rear end (72) of the truck (71). Unless a distance pad is applied, the detector (70) treats the object (80) as if it were still at a distance D from the truck (71). Therefore the truck (71) would collide with the object (80) before the system could ever respond to the situation.
To overcome the problem with actual and calculated ranges, some manufacturers have introduced a correction or pad in the distance calculation formula. However, such a technique has been only partially successful, because of the variety of truck structures. Even though the technique mitigated the problem somewhat, a distance error remains in many installations.